This invention relates to stepper motors such as described within U.S. Pat. No. 6,967,425 entitled “Multi-Functional Electric Stepper Motor Assembly Having Increased Motor Torque” and U.S. Pat. No. 6,879,128 entitled “Method and Apparatus For Independently Controlling Each Phase of a Multi-Phase Step Motor”, which patents are incorporated herein for purposes of reference.
One problem generally associated with such stepper motors is the possibility of motor stall when the torque generated by the associated load exceeds the motor rating.
A further problem occurs when the associated load causes the motor rotor to lead or lag the motor stator to such an extent as to cause the rotor to jump from one stable position to a new stable position, which is known as “cogging”.
When such stepper motors are employed in commercial applications, the torque load generated by the associated equipment is estimated and the rating of stepper motors employed is then selected to exceed the estimated load by as high as fifty percent to defer the onset of such stalling or cogging.
One approach used to defer the occurrence of motor cogging is described within U.S. Pat. No. 5,250,867 entitled “Permanent Magnet Brushless DC Motor Having Reduced Cogging” wherein the motor stator is custom configured.
To employ a motor of equivalent load rating, a feedback circuit including a digital signal processor, such as that described within U.S. Pat. No. 6,121,744 entitled “Control Apparatus for Position Control Motor” and U.S. Pat. No. 7,081,730 entitled “Motor Controller System for Large Dynamic Range of Motor Operation” is usually required.
In most applications, the feedback circuit for preventing stalling is incorporated within the servo-motor circuit, per se, and cannot be used with existing motors
One purpose of the instant invention is to provide a simple arrangement whereby the position of the motor rotor to the motor stator is monitored and controlled on a continuing basis to defer the onset of stalling or cogging at all times of motor operation.
A further purpose of the invention is to provide an add-on rotor-stator control circuit for use with an existing motor arrangement when additional or changing loads are applied, as well as enabling an existing motor to accommodate a load which may from time to time exceed the rating of the motor.